The present invention generally relates axle assemblies and more particularly to an axle assembly having a two piece axle shaft.
Many motor vehicles employ driveline systems wherein rotary power is distributed by a differential to a pair of axle shafts. Typically, axle shafts include a flange that is configured to be mated to a wheel, and a shaft, which couples the flange to the differential. The axle shafts known in the art are typically formed, at least partially, by a combination of forging and machining wherein a single steel billet is shaped to the general configuration of an axle by hot forging and cold extrusion. The final finished form is then produced by a series of secondary machining operation. Construction of axle shafts in this manner is known to have several drawbacks.
One such drawback concerns the overall cost of the axle shaft. As mentioned above, the axle shaft is initially formed in a forging operation so as to provide the axle shaft with a predetermined grain structure. Forging, however, is a relatively expensive process that is typically incapable of net forming axle shafts and other automotive components. Furthermore, several secondary operations, such as straightening, are often necessary prior to the finish machining of the forged axle shaft. The finish machining of an axle shaft usually entails several turning operations, several drilling operations, a hobbing or broaching operation and in most cases, a follow-up heat treating operation. As a result of the cost of the capital equipment, perishable tooling and labor associated with these operations, it is relatively common for the finish machining costs to be more than twice the cost of the axle shaft forging.
Another drawback concerns the weight of the finished axle shaft. As a forging operation is employed to initially form the axle shaft from a steel billet, the axle shaft is formed with a solid shaft between the ends that will ultimately mate to the vehicle wheel and the vehicle differential. Often times, however, the strength that is provided by the solid shaft far exceeds that which is necessary and as such, the additional mass of the solid shaft is undesirable. Removal of this additional mass, however, is typically not practical due to the costs associated with yet another machining operation and/or the impact on other areas of the axle shaft. Assuming, for example, that a drilling operation could be employed to hollow out the shaft, its costs would likely be prohibitive and there would be some concerns that the hole formed would negatively impact portions of the axle shaft, such as the end portion that couples to the differential.
Accordingly, there remains a need in the art for an improved axle shaft that is more easily manufactured and lighter in weight than conventionally forged axle shafts.
In one preferred form, the present invention provides an axle shaft for a differential assembly. The axle shaft includes a shaft structure and a flange structure. The shaft structure has a coupling portion with an engagement surface and the flange structure has a mounting aperture with a contact surface. The mounting aperture is sized to receive the coupling portion to permit the engagement surface and the contact surface to be engaged to one another so as to facilitate transmission of rotary power therebetween. In one embodiment, an interference fit, such as a press fit or a shrink fit, is employed to fix the coupling portion to the mounting aperture and a laser weld is employed to ensure that the shaft and flange structures remain fixedly secured to one another. In another embodiment, the laser weld both secures the shaft and flange structures to one another as well as facilitates the transmission of drive torque therebetween.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.